8

TC7660

CHARGE PUMP DC-TO-DC

VOLTAGE CONVERTER

© 2001 Microchip Technology Inc.

DS21465A

TC7660-7 9/30/96

Figure 6. External Clocking

Figure 7. Lowering Oscillator Frequency

Positive Voltage Multiplication

The TC7660 may be employed to achieve positive

voltage multiplication using the circuit shown in Figure 8. In

this application, the pump inverter switches of the TC7660

or twice the supply voltage minus the combined forward

of 10 mA, it will be approximately 60

Ω.

Figure 8. Positive Voltage Multiplier

Combined Negative Voltage Conversion

and Positive Supply Multiplication

Figure 9 combines the functions shown in Figures 3 and

8 to provide negative voltage conversion and positive volt-

age multiplication simultaneously. This approach would be,

for example, suitable for generating +9V and – 5V from an

perform the pump and reservoir functions, respectively, for

plied positive voltage. There is a penalty in this configuration

which combines both functions, however, in that the source

impedances of the generated supplies will be somewhat

higher due to the finite impedance of the common charge

pump driver at pin 2 of the device.

Figure 9. Combined Negative Converter and Positive Multiplier

Efficient Positive Voltage

Multiplication/Conversion

Since the switches that allow the charge pumping op-

eration are bidirectional, the charge transfer can be per-

formed backwards as easily as forwards. Figure 10 shows

a TC7660 transforming – 5V to +5V (or +5V to +10V, etc.).

The only problem here is that the internal clock and switch-

drive section will not operate until some positive voltage has

been generated. An initial inefficient pump, as shown in

Figure 9, could be used to start this circuit up, after which it

on), or else the diode and resistor shown dotted in Figure 10

can be used to "force" the internal regulator on.

1

2

3

4

8

7

6

5

TC7660

+

V +

+

CMOS

GATE

10

µF

VOUT

10

µF

1 k

Ω

V +

1

2

3

4

8

7

6

5

+

V

+

VOUT

C1

COSC

+

C2

TC7660

1

2

3

4

8

7

6

5

+

V +

VOUT =

(2 V +) – (2 VF)

C1

D1

+

+

C3

C4

VOUT =

– (V+– VF)

C2

TC7660

D2

+

1

2

3

4

8

7

6

5

V+

VOUT =

(2 V+) – (2 VF)

+

C2

D1

D2

+

C1

TC7660